1. Field of the Invention
The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus for polishing a substrate for use in semiconductor devices.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 xcexcm wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus, and such a process is called Chemical Mechanical Polishing (CMP) in which the semiconductor wafers are chemically and mechanically polished while supplying a polishing liquid comprising abrasive particles and chemical solution such as alkaline solution.
In a manufacturing process of a semiconductor device, a thin film is formed on a semiconductor device, and then micromachining processes, such as patterning or forming holes, are applied thereto. Thereafter, the above processes are repeated to form thin films on the semiconductor device. Recently, semiconductor devices have become more integrated, and the structure of semiconductor elements has become more complicated. In addition, the number of layers in multilayer interconnections used for a logical system has been increased. Therefore, irregularities on the surface of the semiconductor device are increased, so that the step height on the surface of the semiconductor device becomes larger.
When the irregularities of the surface of the semiconductor device are increased, the following problems arise. The thickness of a film formed in a portion having a step is relatively small. An open circuit is caused by disconnection of interconnections, or a short circuit is caused by insufficient insulation between the layers. As a result, good products cannot be obtained, and the yield is lowered. Further, even if a semiconductor device initially works normally, reliability of the semiconductor device is lowered after a long-term use.
Thus, in the manufacturing process of a semiconductor device, it is increasingly important to planarize the surface of the semiconductor device. The most important one of the planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, a polishing apparatus is employed. While a polishing liquid containing abrasive particles such as silica (SiO2) therein is supplied onto a polishing surface such as a polishing pad, a substrate such a semiconductor wafer is brought into sliding contact with the polishing surface, so that the substrate is polished.
FIG. 23 of the accompanying drawings show a conventional polishing apparatus for carrying out a CMP process. As shown in FIG. 23, a polishing apparatus 101 having a belt has been used, in addition to a rotary apparatus with a rotatable polishing pad, for planarizing a device surface of a semiconductor wafer W. The polishing apparatus 101 has a flexible endless belt 102 with a resilient polishing pad 105 applied to an outer surface thereof. The belt 102 is wound onto a pair of rollers 103, 104 that rotate about their own axes. A backup plate 109 is positioned along a straight stretch of the belt 102 between the rollers 103, 104 and held against the reverse side of the belt 102. The polishing apparatus 101 has a rotatable top ring 108 disposed in confronting relation to the belt 102 held by the backup plate 109. The top ring 108 presses the semiconductor wafer W against the polishing pad 105 on the belt 102.
In the conventional polishing apparatus having the above structure, the polishing pad 105 applied to the flexible endless belt 102 cannot easily be replaced with a new one. The resilient polishing pad 105 tends to cause polishing in recesses of the semiconductor wafer W to progress, this phenomenon being called xe2x80x9cdishingxe2x80x9d. Attempts to use a fixed abrasive to prevent dishing have been unsuccessful because the belt 102 is flexible.
It is therefore an object of the present invention to provide a polishing apparatus which has a polishing pad that can be replaced easily and which allows a fixed abrasive to be used with ease.
In order to achieve the above object, according to the present invention there is provided a polishing apparatus comprising: a top ring for holding a workpiece to be polished; and a polishing table movable relatively to the top ring, the polishing table having a polishing surface for polishing the workpiece held by the top ring; wherein at least one of the top ring and the polishing table reciprocates linearly in a first direction.
The workpiece typically comprises a semiconductor wafer for manufacturing semiconductor devices.
According to the present invention, the polishing table is movable relatively to the top ring for polishing the workpiece held by the top ring, and at least one of the top ring and the polishing table reciprocates linearly in the first direction, and hence the workpiece can be polished uniformly.
In a preferred aspect, the polishing apparatus further comprises a polishing liquid supply device for supplying a polishing liquid to the polishing surface. The polishing liquid supply device comprises a fluid passage formed in the polishing table for supplying the polishing liquid to the polishing surface. The polishing liquid typically comprises an abrasive liquid containing abrasive particles, but may comprise pure water.
In a preferred aspect, the polishing apparatus further comprises a dresser which reciprocates linearly in a second direction for dressing the polishing surface. The second direction typically intersects the first direction, and preferably perpendicularly to the first direction. The second direction may be in conformity with the first direction, allowing the dresser to sweep debris off the polishing surface.
Since the dresser reciprocates linearly in the second direction, it can dress the polishing surface uniformly.
In a preferred aspect, a plurality of the dressers are provided in combination with the top ring.
The dressers may be of different types and may selectively be used for dressing the polishing surface differently. If the dressers are disposed one on each side of the top ring, then the distance that the polishing table reciprocates linearly in the first direction for being dressed by the dressers may be reduced, thus making the polishing apparatus smaller in size.
The top ring preferably reciprocates linearly in a third direction intersecting the first direction. The third direction is typically the same as the second direction.
Inasmuch as the top ring reciprocates linearly in the third direction intersecting the first direction, the workpiece can be polished uniformly without using the polishing surface locally.
In a preferred aspect, the top ring is arranged to rotate the workpiece held thereby with respect to the polishing table. The top ring should be rotated at a speed up to 10 revolutions per minute. Because the top ring rotates the workpiece held thereby with respect to the polishing table, the surface, being polished, of the workpiece is prevented from being locally scratched or damaged.
The polishing surface should preferably have a groove formed therein for discharging a waste material from the polishing surface. The waste material includes ground-off material produced when the workpiece is polished, and the used polishing liquid. The groove is typically arranged to eject a cleaning liquid or draw the waste material under vacuum.
The polishing table may have a plurality of polishing surfaces having different levels of coarseness. One of the polishing surfaces may comprise a fixed abrasive. Particularly, one of the polishing surfaces which is used to roughly polish the workpiece should comprise a fixed abrasive.
With the polishing table which comprises a plurality of polishing surfaces having different levels of coarseness, the polishing table is capable of polishing the workpiece under conditions that are suitable for the shape and properties of the surface, to be polished, of the workpiece.
In a preferred aspect, the polishing apparatus further comprises a linear motor for reciprocating linearly at least one of the top ring and the polishing table in the first direction.
Preferably, the polishing table is arranged to reciprocate linearly in the first direction, and the polishing apparatus further comprises a linear guide supporting the polishing table under a fluid pressure.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.